Transcript File - Garbally Chemistry

Chapter 22
Families of Organic Compounds
Tetrahedral Carbon
Compounds.
• In tetrahedral compounds the atom or group of
atoms responsible for the characteristic properties
of the compound is attached to a tetrahedral
carbon atom.
– Chloroalkanes
– Alkanes
– Alcohols
Chloroalkanes
Chloroalkanes-One or more of the H atoms
in the alkane replaced by a Cl atom.
-Synthesised in the Lab
-Used as solvents
-Not soluble in water(no polarity).
-Dissolve in non-polar solvents like cyclohexane.
STRUCTURAL ISOMERISM IN HALOGENOALKANES
Different structures are possible due to...
Different positions for the halogen and branching of the carbon chain
1-chlorobutane
2-chloro-2-methylpropane
2-chlorobutane
1-chloro-2-methylpropane
Chloroalkanes
Chloroalkanes
• One or more of the hydrogen atoms in an alkane molecule
has been replaced by a chlorine atom, e.g.
• Chloromethane
- CH3Cl
• Dichloromethane - CH2Cl2
• Trichloromethane - CHCl3
• Tetrachloromethane - CCl4
Chloromethane
Dichloromethane
Trichloromethane
Tetrachloromethane
Chloroethane
1,1-dichloroethane
1,2-dichloroethane
Naming chloroalkanes
• Last part of name comes from base alkane
on which the molecule is built, e.g.
chloroethane [2 carbons]
• Number of chlorine atoms indicated by
prefix mono, di, tri, tetra etc. in front of
chloromethane, e.g. trichloromethane
• Position of each chlorine atom given by a
number before the name, e.g.
1,2,2-trichloropropane
1,2,2-trichloropropane
Physical properties
• Physical state: Liquid, except for
chloromethane and chloroethane, which are
gases at room temperature
• Boiling points higher than the
corresponding alkanes, due to polar C-Cl
bond(s)
Physical properties
• Not soluble in water
• Soluble in non-polar solvents such as
cyclohexane
Uses of chloroalkanes
• Because of their lack of polarity, they are
useful solvents, e.g. for
• removing grease and oil from machinery
• removing oil etc. from clothes - dry
cleaning
Alcohols
• Alcohol’s form a homologous series of compounds.
• The -OH group called the hydroxyl group is the functional
group of the alcohols.
Alcohols
Alcohols
•
•
•
•
•
•
Methanol CH3OH
Ethanol C2H5OH
Propan-1-ol C3H7OH
Propan-2-ol C3H7OH
Butan-1-ol C4H9OH
Butan-2-ol C4H9OH
Methanol CH3OH
Ethanol C2H5OH
Propan-1-ol C3H7OH
Butan-1-ol C4H9OH
Propan-2-ol CH3CH(OH)CH3
Butan-2-ol CH3CH(OH)C3H7
Classification of alcohols
1. Primary alcohol: contains one carbon
atom directly attached to the carbon that
contains the hydroxyl group, e.g.
propan-1-ol
2. Secondary alcohol: contains two carbon
atoms directly attached to the carbon that
contains the hydroxyl group, e.g.
propan-2-ol
Physical properties
• Physical state: Liquid
• Boiling points much higher than the
corresponding alkanes, due to polar OH
group
Physical properties
Solubility of methanol in
• (i) cyclohexane – not very soluble
methanol is polar cyclohexane is not
• (ii) water - completely soluble
because it is polar.
• As alcohol molecule gets bigger the polar
part becomes less significant so the alcohol
becomes less soluble in water and more
soluble in cyclohexane
Butan-1-ol is
–(i) soluble in cyclohexane
–(ii) not very soluble in water
• The polar OH group is becoming less
significant as the molecule gets bigger
Comparison with water
• Both have polar OH groups
• Alcohols have a non-polar part
• Both form hydrogen bonds between their
molecules
• Water is more polar and has a greater
capacity to form hydrogen bonds and so has
a higher boiling point than methanol or
ethanol
Methanol
• Methanol: is toxic (can cause blindness, insanity and death)
• It is added to industrial alcohol to prevent people drinking
it. This mixture is called methylated spirits.
• The methanol acts as a denaturing agent – it renders a
substance unfit for purpose without destroying the
usefulness or applications of the substance. A purple dye is
often added as a warning.
Ethanol
• Ethanol: is produced by fermentation. Fruits provide the
sugar and yeast may need to be added.
• The enzyme zymase in yeast catalyses the reaction.
C6H12O6
2C2H5OH
+
2CO2
Alcoholic Drinks
Ingredient
Drink
Grapes
Wine
% (v/v)
alcohol
12
Apples
Cider
4.5
Malted
grain
Beer
5
Ethanol
• To produce drinks of higher alcohol
concentration the fermented liquids must be
distilled.
• Spirits (whiskey, brandy, gin, vodka)
contain 40% alcohol.
Gasohol
• Ethanol obtained from sugar cane is used
for making gasohol in Brazil. This is then
used as a fuel.
Uses of ethanol
1. Alcoholic drinks
2. Fuel
3. Solvent (can dissolve both polar and nonpolar solutes)
Primary Secondary and
Tertiary
• Primary Alcohol -one C attached to the
C which has the –OH group.
• Secondary Alcohol -Two C attached to the
C which has the –OH group.
• Tertiary Alcohol -Three C attached to the
C which has the –OH group.
Examples of Alcohol’s
Methanol-added to industrial alcohol to
prevent consumption.
Ethanol-Used in alcoholic drinks, as a fuel and
as a solvent.
Ethanol is produced by fermentation.
Yeast
C6H12O6 -------->
Zymase
2C2H5OH
+
2CO2
Physical Properties of Alcohol’s
Boiling points
Alcohol’s have a higher boiling point than corresponding
alkanes. This is due to Hydrogen bonding between the
Alcohol molecules.
Hydrogen bonding between
alcohol molecules
Solubility of Alcohols
Hydrogen bonding also results in Alcohol’s
been soluble in water.(C1-C3)
This solubility decreases as the length of the
Carbon chain increases. This is due to the
polar -OH group(which is responsible for
solubility) been counteracted by the larger
insoluble alkyl group
Planar Carbon Compounds.
Alkenes
Aldehydes
Carboxylic Acids
Aromatic Compounds
Note.
These compounds have double bonds
Alkynes
Ketones
Esters
Aldehydes
An aldehyde is a compound containing a carbonyl
group with at least one hydrogen attached to it.
• Functional Group –CHO
• Strongly Polar
(Carbonyl group)
Formal names for aldehydes include the prefix from the alkyl group
and the suffix -al.
Two of the simplest aldehydes are
Aromatic aldehydes include oil of almonds, vanillin, and oil of
cinnamon.
Aldehydes
Aldehydes
• Methanal HCHO
• Ethanal
CH3CHO
• Propanal C2H5CHO
• Butanal
C3H7CHO
Methanal
Ethanal
Propanal
Butanal
Physical properties
• Physical state: Liquid, except methanal,
which is a gas at room temperature
• Boiling points higher than the
corresponding alkanes, due to polar +C =
O- group, but lower than the corresponding
alcohols
Physical properties
• Short chain aldehydes are soluble in
water due to the polar carbonyl group
• As the number of carbon atoms in a
molecule of the ester increases, solubility in
water decreases, while solubility in
cyclohexane increases
Benzaldehyde
• Aromatic aldehyde
• Found in almond
kernels
Boiling points and solubility of
the aldehydes
Boiling points
Not possible to form Hydrogen Bonds
between the aldehyde molecules. There is
however Dipole-Dipole bonds between the
aldehyde molecules.
This results in the aldehydes having boiling
point higher than corresponding alkanes but
lower than corresponding alcohol.
Eg Ethanal Bp = 21C
Ethanol Bp = 78C
Compare Boiling Points
Molecule
Type
Boiling point (°C)
CH3CH2CH3
alkane
-42
CH3CHO
aldehyde
+21
CH3CH2OH
alcohol
+78
Notice that the aldehyde (with dipole-dipole attractions as well as dispersion forces) has a boiling
point higher than the similarly sized alkane which only has dispersion forces.
However, the aldehyde's boiling point isn't as high as the alcohol's.
In the alcohol, there is hydrogen bonding as well as the other two kinds of intermolecular
attraction.
Although the aldehydes and ketones are highly polar molecules, they don't have any hydrogen
atoms attached directly to the oxygen, and so they can't hydrogen bond with each other.
• Methanal- only aldehyde that is a gas at room
Temperature.(also called Formaldehyde)
• Lower members of the aldehyde’s are soluble in H20
and like the alcohol’s will dissolve in both polar and
non-polar substances. This is due to H bonding
between the O atom in the carbonyl and the H atom of
the water molecule.
• Like the alcohol’s, the solubility in water decreases
with the length of the carbon chain.
Ketones
• Functional group R-CO –R
• Physical properties similar to the Aldehydes
due to the Dipole-Dipole forces between the
Ketone molecules.
• Solubility similar to the Aldehydes.
• Since Propanone(acetone) and Butanone can
act as solvents in both polar and non polar
solvents they are widely used in industry
In ketones, the carbonyl group has two hydrocarbon groups attached.
Notice that ketones never have a hydrogen atom attached to the carbonyl
group.
Propanone is normally written CH3COCH3. Notice the need for
numbering in the longer ketones. In pentanone, the carbonyl group could
be in the middle of the chain or next to the end - giving either pentan-3one or pentan-2-one.
Ketones
Ketones
• Propanone CH3COCH3
• Butanone C2H5COCH3
Propanone
Butanone
Physical properties
• Physical state: Butanone and propanone are
liquids at room temperature
• Boiling points higher than the corresponding
alkanes, due to polar +C = O- group, but
lower than the corresponding alcohols
• Short chain ketones such as propanone are
soluble in water due to the polar carbonyl
group
• Ketones are soluble in non-polar solvents
such as cyclohexane
Uses of propanone
• Propanone is used as a solvent (e.g. In nail
varnish remover)
Carboxylic acids
Carboxylic Acids.
Functional Group
R- COOH
Examples of Carboxylic Acids
Methanoic Acid
Ethanoic Acid
Propanoic Acid
HCOOH
CH3COOH
C2H5COOH
Carboxylic acids
• Methanoic acid HCOOH
• Ethanoic acid
CH3COOH
• Propanoic acid C2H5COOH
• Butanoic acid
C3H7COOH
Methanoic acid
HCOOH
Ethanoic acid
CH3COOH
Propanoic acid
C2H5COOH
Butanoic acid
C3H7COOH
Physical properties
• Physical state: Methanoic acid and ethanoic
acid are liquids, while propanoic acid and
butanoic acid are solids
• Short chain carboxylic acids are soluble in
water due to the polar COOH group
• Carboxylic acids are soluble in non-polar
solvents such as cyclohexane
Boiling points of carboxylic acids
• Boiling points higher than the
corresponding alcohols
• This is because carboxylic acids form
dimers, where two carboxylic acid
molecules are held together by two
hydrogen bonds
• This is possible due to polarity in both the
C=O and O-H bonds in each carboxylic acid
molecule
Ethanoic acid dimer
δ-
δ+
δ-
δ+
δ+
δ-
δ+
δ-
Occurrence and uses
• Methanoic acid is found in the sting of ants
and nettles
• Ethanoic acid is the principal acid in
vinegar
• Ethanoic acid is used in the manufacture of
cellulose acetate
• Propanoic acid, benzoic acid and their salts
(e.g. sodium benzoate) are used as food
preservatives
Examples of Carboxylic acid and
uses
• Methanoic acid(formic acid) sting of nettles
and ants
• Ethanoic acid(acetic acid)-vinegar,Cellulose
acetate used in varnishes,laquers,
photographic film, rayon
• Propanoic acid, Benzoic acid-Preservatives
• Butanoic acid- smell of rancid butter,smelly
socks
Examples of carboxylic acids
The name counts the total number of carbon atoms in the longest chain including the one in the -COOH group. If you have side groups attached to the
chain, notice that you always count from the carbon atom in the -COOH group
as being number 1
Solubility and Boiling Points
Boiling points
Ethanoic Acid Higher Bp/Mp than
corrisponding Alcohol.Why?
This is due to the effects of Hydrogen
Bonding.
In pure acid the molecules
group together to form clusters of
dimers(two molecules) held together by
2 Hydrogen Bonds.
Solubility
Soluble in Water due to their ability to form
Hydrogen bonds with water.This solubility
decreases with increasing length of the
carbon chain.
Esters
Esters
Esters are formed by the reaction of a carboxylic acid with an
alcohol e.g.
CH3COOH
+
Ethanoic acid
CH3OH
Methanol
=
CH3COOCH3 + H2O
Methyl ethanoate
Naming esters: methyl ethanoate
• The first part of the ester name comes from
the parent alcohol with the - anol changed
to – yl and the second part of the name
comes from the parent acid with the - oic
acid changed to – oate.
Methyl methanoate
HCOOCH3
Ethyl methanoate HCOOC2H5
Methyl ethanoate CH3COOCH3
Ethyl ethanoate CH3COOC2H5
Physical properties
• Physical state: Liquid
• Boiling points higher than the
corresponding alkanes, but lower than the
corresponding alcohols
Physical properties
• Soluble in water and non-polar solvents
such as cyclohexane
• As the number of carbon atoms in a
molecule of the ester increases, solubility in
water decreases, while solubility in
cyclohexane increases
Occurrence and uses of esters
• Occur naturally in fruits – are responsible
for their flavours • and flowers – are responsible for their
pleasant smells
• Fats and oils are naturally occurring esters
of long chain carboxylic acids
• Ethyl ethanoate is used as a solvent for
printing inks and paints
Esters.
Functional Group R-COO-R
Alcohol + Carboxylic Acid

Ester + Water
This reaction is called a condensation reaction since it results in the loss of
a water molecule
Lower members of the Ester family are volatile liquids with Fruity smell.
-Low Bp because H bonds are not formed with each other.
-Polar molecules that can form H bonds with Water.
Lower members(up to C-5) are fairly soluble in water
Polyester-millions of ester molecules linked together
Solid ester = Fat
Liquid Ester = Oil
Aromatic compounds
• Aromatic compounds contain a Benzene
ring.
• Benzene itself is carcinogenic though many
aromatic compounds are not dangerous.
• Form basis of many pharmaceutical
compounds, dyes detergents, herbicides,
disinfectants e.t.c.
STRUCTURE OF BENZENE - DELOCALISATION
The theory suggested that instead of three localised (in one position) double bonds,
the six p (p) electrons making up those bonds were delocalised (not in any one
particular position) around the ring by overlapping the p orbitals. There would be no
double bonds and all bond lengths would be equal. It also gave a planar structure.
6 single bonds
STRUCTURE OF BENZENE - DELOCALISATION
The theory suggested that instead of three localised (in one position) double bonds,
the six p (p) electrons making up those bonds were delocalised (not in any one
particular position) around the ring by overlapping the p orbitals. There would be no
double bonds and all bond lengths would be equal. It also gave a planar structure.
6 single bonds
one way to overlap
adjacent p orbitals
STRUCTURE OF BENZENE - DELOCALISATION
The theory suggested that instead of three localised (in one position) double bonds,
the six p (p) electrons making up those bonds were delocalised (not in any one
particular position) around the ring by overlapping the p orbitals. There would be no
double bonds and all bond lengths would be equal. It also gave a planar structure.
6 single bonds
one way to overlap
adjacent p orbitals
another
possibility
STRUCTURE OF BENZENE - DELOCALISATION
The theory suggested that instead of three localised (in one position) double bonds,
the six p (p) electrons making up those bonds were delocalised (not in any one
particular position) around the ring by overlapping the p orbitals. There would be no
double bonds and all bond lengths would be equal. It also gave a planar structure.
6 single bonds
one way to overlap
adjacent p orbitals
another
possibility
delocalised pi
orbital system
STRUCTURE OF BENZENE - DELOCALISATION
The theory suggested that instead of three localised (in one position) double bonds,
the six p (p) electrons making up those bonds were delocalised (not in any one
particular position) around the ring by overlapping the p orbitals. There would be no
double bonds and all bond lengths would be equal. It also gave a planar structure.
6 single bonds
one way to overlap
adjacent p orbitals
another
possibility
This final structure was particularly stable and
resisted attempts to break it down through normal
electrophilic addition. However, substitution of any
hydrogen atoms would not affect the delocalisation.
delocalised pi
orbital system
STRUCTURE OF BENZENE
STRUCTURE OF BENZENE
ANIMATION
The animation doesn’t work on early versions of Powerpoint
WHY ELECTROPHILIC ATTACK?
Theory
The high electron density of the ring makes it open to attack by electrophiles
HOWEVER...
Because the mechanism involves an initial disruption to the ring
electrophiles will have to be more powerful than those which react
with alkenes.
A fully delocalised ring is stable so will resist attack.
Aromatic compounds
Aromatic compounds
• Aromatic compounds are compounds which
contain a benzene ring in their molecules
Aromatic hydrocarbons
• Benzene C6H6
• Methylbenzene C7H8
• Ethylbenzene C8H10
Benzene
Benzene molecule
• The six carbon-carbon bonds in benzene are
identical, intermediate in length between
double and single bonds
Sigma bonding in benzene
• Six carbon atoms joined to form a
hexagonal planar ring.
• Each carbon has four valence electrons
• One of these is used to form a bond with a
hydrogen atom.
• Two other electrons are used to form sigma
bonds with the carbon atoms on either side.
What the circle means
• The 6 valence electrons not involved in
sigma bonding are shared between the six
carbon atoms in the molecule
• not localised into 3 double bonds
• For convenience the C and H atoms are not
shown
• Ring in centre indicates a delocalised pi
bond
Methylbenzene
Ethylbenzene
Physical properties
• Physical state: Benzene. methylbenzene and
ethylbenzene are liquids
• Insoluble in water
• Soluble in non-polar solvents such as
cyclohexane
Uses
• Methylbenzene is used as an industrial
solvent
Range and scope of aromatic
chemistry
• Pharmaceutical compounds, e.g. Morphine
• Herbicides, e.g. Diuron
• Detergents, e.g. Sodium
dodecylbenzenesulfonate
• Dyes, e.g. Martius Yellow
Aromatic acid-base indicators
• The acid-base indicators phenolphthalein
and methyl orange are also aromatic
compounds
Phenolphthalein
orange
Methyl
Aromatic compounds and cancer
• Some aromatic compounds are
carcinogenic, e.g. Benzene
• However, not all aromatic compounds are
carcinogenic; aspirin is an example
Organic Compounds
• Many organic compounds are found free in nature.
• Examples
–
–
–
–
Benzaldehyde(Almonds)
Caffeine(coffee)
Nicotine(cigarettes)
Pharmaceutical compounds(Aspirin, Iboprofen, Morphine,
Paracetamol, Penicillin)
– Food Flavouring(Vanilla)
– insecticides(DDT, Diuron, Naphthalene)
Steam Distillation
• A technique called steam distillation is used to separate oils
from plants.
• It involves carrying out distillation in a current of steam .
The main purpose is to avoid too high a temperature during
distillation as a high temperature may destroy the plant
material.
• It is found that the mixture of steam and oil distils below the
boiling point of water and well below the boiling point of
the oil in the plant.
• The mixture of oil and steam is then passed through a
Liebeg condenser and allowed to stand. The oil floats to the
top.
Apparatus for steam distillation
Field of Lavender
Emulsion
• An emulsion is where the oil droplets are dispersed
throughout the water.
• An organic solvent must be added that dissolves the
oil(e.g. cyclohexane) but does not mix with the water. This
is then separated and the solvent allowed to evaporate.
This process is called solvent extraction.
– Experiment: To extract clove oil from cloves by
steam distillation
– See Page 357(book)